Lubricants with enhanced thermal conductivity containing nanomaterial for automatic transmission fluids, power transmission fluids and hydraulic steering applications

ABSTRACT

A lubricant composition having an enhanced thermal conductivity, up to 80% greater than its conventional analogues, and methods of preparation for these fluids are identified. One preferred composition contains a base oil, nanomaterial, and a dispersing agent or surfactant for the purpose of stabilizing the nanomaterial. One preferred nanomaterial is a high thermal conductivity graphite, exceeding 80 W/m in thermal conductivity. The graphite is ground, milled, or naturally prepared to obtain a mean particle size less than 500 nm in diameter, and preferably less than 100 nm, and most preferably less than 50 nm. The graphite is dispersed in the fluid by one or more of various methods, including ultrasonication, milling, and chemical dispersion. Carbon nanostructures such as nanotubes, nanofibrils, and nanoparticles are another type of graphitic structure useful in the present invention. Other high thermal conductivity carbon materials are also acceptable. To confer long-term stability, the use of one or more chemical dispersants or surfactants is useful. The thermal conductivity enhancement, compared to the fluid without graphite, is proportional to the amount of nanomaterials added. The graphite nanomaterials contribute to the overall fluid viscosity, partly or completely eliminating the need for viscosity index improvers and providing a very high viscosity index. Particle size and dispersing chemistry is controlled to get the desired combination of viscosity and thermal conductivity increase from the base oil while controlling the amount of temporary viscosity loss in shear fields. The resulting fluids have unique properties due to the high thermal conductivity and high viscosity index of the suspended particles, as well as their small size.

This application is a Continuation-In-Part of copending U.S. applicationSer. No. 10/737,731 filed on Dec. 16, 2003 which claims priority fromU.S. application Ser. No. 10/021,767 filed on Dec. 12, 2001 which claimspriority from U.S. Provisional Application Ser. No. 60/254,959 filed onDec. 12, 2000; PCT Application S.N. PCT/US02/16888 filed on May 30,2002; U.S. nonprovisional application Ser. No. ______ filed on Dec. 8,2003; and claims priority from U.S. Provisional Application Ser. No.60/433,798 filed on Dec. 16, 2002 all of which are incorporated byreference in their entirety.

This application is part of a government project, Contract No.W031-109-ENG-38 by the Department of Energy. The Government has certainrights in this invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to the field of providing lubricants andfunctional fluids containing nanomaterial dispersed within automatictransmission fluids, power transmission fluids, and hydraulic steeringfluids which exhibit enhanced thermal conductivity as compared toconventional fluids without the nanomaterial dispersions.

2. Description of the Prior Art

Lubricants and coolants of various types are used in equipment and inmanufacturing processes to remove waste heat, among other functions.Traditionally, water is most preferred for heat removal, however, toexpand it's working temperature range, freezing point depressants suchas ethylene glycol and/or propylene glycol are added, typically atlevels above 10% concentration by volume. For example, automotivecoolant is typically a mixture of 50-70% ethylene glycol, and theremainder is water. The thermal conductivity of the freezing pointdepressed fluid is then about ⅔ as good as water alone, as illustratedin Table 1. In many processes and applications, water can not be usedfor various reasons, such as corrosion, temperature restriction, etc.,and then a type of oil, e.g., mineral oil, polyalphaolefin, estersynthetic oil, ethylene oxide/propylene oxide synthetic oil,polyalkylene glycol synthetic oil, etc. is used. The thermalconductivity of these oils, is typically 0.12 to 0.16 W/m at roomtemperature, and thus they are inferior as heat transfer agents towater, since water has a much higher thermal conductivity, 0.61 W/m asset forth in Table 1. Usually these oils have many other importantfunctions, and they are carefully formulated to perform to exactingspecifications for example for friction and wear performance, lowtemperature performance, fuel efficiency performance etc. Oftendesigners will desire a fluid with higher thermal conductivity than theconventional oil, but are restricted to oil due to the many otherparameters the fluid must meet.

TABLE 1 Thermal conductivity of various materials (at room temperature)Thermal Conductivity Material (W/m) Mineral oil 0.13 Typical fully-0.12-0.16 formulated engine oil Ethylene glycol 0.253 Water 0.613Commercial 0.40 antifreeze Graphite  80-700

The use of graphite in fluids such as lubricants is well known. Thegraphite is added as a friction reducing agent, which also carries someof the load imposed on the working fluid, and therefore helps to reducesurface damage to working parts. In order to be low friction, it is wellknown that the graphite layered structure must contain some water orother material to create the interlayer spacing and thereby lamellarstructure. There are various commercially available graphitesuspensions, e.g., from Acheson Colloid Co., which are specificallyintended for use in lubricants. The size of the particles is varied fordifferent dispersions, but the minimum average size for commerciallyavailable products is in the submicron range, typically mean as 500-800nm (nanometers). The thermal advantage of the graphite is nor mentionedin the sales literature, nor is the product sold or promoted for itsthermal conductivity property.

While there have been various patents filed on lubricants containinggraphite, e.g. U.S. Pat. No. 6,169,059, there are none whichspecifically rely on graphite to improve the thermal conductivity of thefluid formulated for specific applications. Furthermore, there are nonewhich teach specifically the use of nanometer-sized graphite with meanparticle size much significantly less than 1000 nm in order to increasethermal conductivity and that reducing particle size improves thermalconductivity. While graphite-containing automotive engine oil was oncecommercialized (Arco graphite), the potential to use graphite as a heattransfer improving material in this oil was not realized. The particlesize of graphite used was larger (mean greater than one micron) than forthe instant invention. As a result, the graphite had some settlingtendency in the fluid. Graphite of this size also significantly affectsthe friction and wear properties of the fluid, and heretofore has beenused to reduce friction and improve wear performance of the fluid, e.g.in metalworking fluids. On the other hand, the use of graphite inlubricants for recirculating systems was made unpopular, partly due toevidence that micron size graphite could “pile up” in restricted flowareas in concentrated contacts, thereby leading to lubricant starvation.No recognition of effect of graphite particle size on this phenomena wasmade.

Previously, naturally formed “nano-graphites” have not been available inthe marketplace at all. Recently, Hyperion Catalysis International, Inc.commercialized carbon nanotubes or so-called carbon fibrils, which havea graphitic content, e.g., U.S. Pat. No. 5,165,909. Carbon nanotubes aretypically hollow graphite-like tubules having a diameter of generallyseveral to several tens nanometers. They exist in the form either asdiscrete fibers or aggregate particles of nanofibers. The thermalconductivity of the Hyperion Catalysis International, Inc. material isnot stated in their product literature. However, the potential of carbonnanotubes to convey thermal conductivity in a material is mentioned intheir patents, U.S. Pat. No. 5,165,909. Actual measurement of thethermal conductivity of the carbon fibrils they produced was not givenin the patent, so the inference of thermal conductivity is general andsomewhat speculative, based on graphitic structure.

Bulk graphite with high thermal conductivity is available from PocoGraphite as a graphite foam, with thermal conductivity higher than 100W/m, and is also available from the Carbide/Graphite Group, Inc.Graphite powders can be obtained from UCAR Carbon Company Inc., withthermal conductivity 10-500 W/m, and typically >80 W/m, and from CytecCarbon Fibers LLC, with thermal conductivity 400-700 W/m. These bulkmaterials must be reduced to a nanometer-sized powder by various methodsfor use in the instant invention.

Utilization of these inexpensive sources of nanomaterials have not beenreleased in lubrication formulations before and a point of novelty inthe instant invention is the ability to reduce the graphite to producean inexpensive nanomaterial having a particle size suitable for longterm dispersion in lubricating compositions and the method of dispersingsame.

Automatic transmission fluids, (“ATF”), power transmission fluids andhydraulic steering fluids have stringent requirements for viscosity,stability to oxidation, temperature and shear, low temperature fluidity,and static and dynamic coefficient of friction and their relative levelsover many shift cycles. Additionally, the heat transfer requirements intransmissions and pumps are significant. It is generally necessary touse some form of cooling for the transmission fluid, and some designs oftransmissions are prevented due to insufficient capability to eliminatewaste heat. Because of the friction control requirements, and therelatively large particle size of conventional graphite dispersions, theuse of graphite in these fluids is not known.

While the present invention is applicable in automatic transmissionfluids, (ATF), power transmission fluids and hydraulic steering fluids,the examples and further discussion will focus on automatic transmissionfluids; however, the claims are applicable to the power transmissionfluids, hydraulic steering fluids, and other types of oil basednoncompressible fluids as well.

SUMMARY OF THE INVENTION

In this invention, automatic transmission fluids of enhanced thermalconductivity are prepared by dispersing nanometer-sized carbonnanomaterials of thermal conductivity higher than 80 W/m into the fluidThe term carbon nanomaterials used in this invention refers to graphitenanoparticles, carbon nanotubes or fibrils, and other nanoparticles ofcarbon with graphitic structure. Stable dispersion is achieved byphysical and chemical treatments.

For example, the instant invention provides a method for making acomposition for an automatic transmission fluids that have enhancedthermal conductivity, up to 80% greater than their conventionalanalogues. One preferred composition contains an effective amount of atleast one base oil such as mineral oil, hydrocracked mineral oil withhigh viscosity index, vegetable derived oils, polyalphaolefins,poly-internal-olefins, polyalkylglycols, polycyclopentadienes, propyleneoxide or ethylene oxide based synthetics, silicone oils, phosphateesters or other synthetic esters, or any suitable base oil; an effectiveamount of at least one type of nanomaterial, preferably graphitenanoparticle or carbon nanotubes, and an effective amount of at leastone dispersing agents or surfactants for the purpose of stabilizing thenanoparticles.

One preferred nanomaterial is a high thermal conductivity graphite,exceeding 80 W/m in thermal conductivity, and ground, milled, ornaturally prepared with mean particle size less than 500 nm in diameter,and preferably less than 100 nm, and most preferably less than 50 nm.The graphite is dispersed in the fluid by one or more of variousmethods, including ultrasonication, milling, and chemical dispersion. Itis contemplated that nanoparticles can be selected from any metal fromthe Group IV elements, such as carbon materials (carbon nanotubes,fullerenes, graphite, amorphous carbon, carbon particles, carbon fibrilsand combinations thereof, etc.), silicone carbide, and clay materials,metal (including transition metals) particles (such as silver, copper,aluminum, etc.), metal oxides, alloy particles, and combinations thereofmay be applicable to the instant invention.

Carbon nanotubes with a graphitic structure are another preferred typeof nanomaterial or particles. Other high thermal conductivity carbonmaterials are also acceptable as long as they meet the thermalconductivity and size criteria set forth heretofore.

To confer long-term stability, an effective amount of one or morechemical dispersants or surfactants is preferred, although a specialgrinding procedure in base oil will also confer long term stability. Thethermal conductivity enhancement, compared to the fluid withoutgraphite, is proportional to the amount of nanomaterials added. Thegraphite nanoparticles or nanotubes contribute to the overall fluidviscosity, partly or completely eliminating the need for viscosity indeximprovers and providing a very high viscosity index. Particle size anddispersing chemistry is controlled to get the desired combination ofviscosity and thermal conductivity increase from the base oil whilecontrolling the amount of temporary viscosity loss in shear fields. Theresulting fluids have unique properties due to the high thermalconductivity and high viscosity index of the suspended particles, aswell as their small size.

The present invention provides at a minimum, a fluid of lubricantcontaining less than 10% by weight graphite nanoparticles. Preferably,however, a minimum of one or more chemical dispersing agents and/orsurfactants is also added to achieve long term stability.

The term dispersant in the instant invention refers to a surfactantadded to a medium to promote uniform suspension of extremely fine solidparticles, often of colloidal size. In the lubricant industry the termdispersant is generally accepted to describe the long chain oil solubleor dispersible compounds which function to disperse the “cold sludge”formed in engines. The term surfactant in the instant invention refersto any chemical compound that reduces surface tension of a liquid whendissolved into it, or reduces interfacial tension between two liquids orbetween a liquid and a solid. It is usually, but not exclusively, a longchain molecule comprised of two moieties; a hydrophilic moiety and alipophilic moiety. The hydrophilic and lipophilic moieties refer to thesegment in the molecule with affinity for water, and that with affinityfor oil, respectively. These two terms, dispersant and surfactant, aremostly used interchangeably in the instant invention for often asurfactant has dispersing characteristics and many dispersants have theability to reduce interfacial tensions.

The particle-containing fluid of the instant invention will have athermal conductivity higher than the neat fluid, wherein the term ‘neat’is defined as the fluid before the particles are added.

The fluid can have other chemical agents or other type particles addedto it as well to impart other desired properties, e.g. friction reducingagents, antiwear or anticorrosion agents, detergents, antioxidants,dispersants to define a lubricant composition suitable for use invehicle applications or the like. Furthermore, the term fluid in theinstant invention is broadly defined to include pastes, gels, greases,and liquid crystalline phases in either organic or aqueous media,emulsions and microemulsions.

For instance, U.S. Pat. No. 4,029,587 by Koch teaches the use of avariety additives for functional fluids applicable to the presentinvention and is hereby incorporated by reference in its entirety.Moreover, U.S. Pat. No. 4,116,877 by Outten et al. teaches the use of avariety additives for hydraulic fluids such as automatic transmissionfluids and power steering fluids applicable to the present invention andis hereby incorporated by reference in its entirety.

As set forth above, the preferred carbon nanomaterials are selected fromgraphitic carbon structures with bulk thermal conductivity exceeding 80W/m. A preferred form of carbon nanomaterials is carbon nanotubes.Another preferred form of carbon nanomaterials is high thermalconductivity graphite. A preferred form of the high thermal conductivitygraphite is Poco Foam from Poco Graphite. Another preferred form of highthermal conductivity graphite is graphite powders from UCAR CarbonCompany Inc. Still another preferred form of high thermal conductivitygraphite is graphite powders from Cytec Carbon Fibers LLC. Still anotherpreferred form of graphite is bulk graphite from The Carbide/GraphiteGroup, Inc.

Of course, one of the major drawbacks concerning commercial use of thecarbon nanotubes and other prepared carbon structures is the cost ofpreparation and availability of same for commercial applications. Theinstant invention has resulted in the development of a method ofreducing very inexpensive graphite to a nanomaterial comprisingparticles, fabrils and flakes suitable for use and long term dispersionin lubricant compositions.

The carbon nanomaterial containing dispersion may also contain a largeamount of one or more other chemical compounds, such as polymers,antiwear agents, friction reducing agents, anti-corrosion agents,detergents, metal passivating agents, antioxidants, antifoaming agents,corrosion inhibitors, pour point depressants, and viscosity indeximprovers that are not for the purpose of dispersing, but to achievethickening or other desired fluid characteristics.

Furthermore, the carbon nanomaterial dispersion can be pre-sheared, in aturbulent flow, such as a nozzle, or high pressure fuel injector,ultrasonic device, or mill in order to achieve a stable viscosity. Thismay be especially desirable in the case where carbon nanotubes with highaspect ratio are used as the graphite source, since they, even more thanspherical particles, will thicken the fluid but loose viscosity whenexposed in turbulent flows such as the flow regime in engines.Pre-shearing, e.g. by milling, sonicating, or passing through a smallorifice, such as in a fuel injector, is a particularly effective way todisperse the particles and to bring them to a stable size so that theirviscosity increasing effect will not change upon further use.

The milling process itself, or other pre-shearing process, can have arather dramatic effect on the long term dispersion stability.

A novel method has been developed whereby graphite particles are milledto form a thick pasty liquid of particles with mean size less than 500nanometers in diameter. The pasty liquid is then used as concentrate toprepare lubricants of various viscosity grades, and can be easilydiluted to make a fluid with suitable viscosity for an automatictransmission fluid. A very effective paste can be made by mixingparticles in a viscous base fluid in a loading of 5 to 20% by weight andmilling for a period of several hours. The base fluid preferablycontains from 20% up to 100% of the dispersant/surfactant mixture withthe remainder being natural, synthetic, or mineral base oil. Once thethermally conductive concentrate prepared by milling is diluted toliquid consistency with base oil and other transmission fluidcomponents, the entire fluid can (optionally) be passed through a smallorifice to further increase the uniformity and decrease the size ofdispersed particles.

An important aspect of this invention is that the final ATF compositionshould be prepared to give an acceptable lubricant film thickness at themaximum shear rate and temperature of use in the target transmission.The maximum concentration of particles in the final (diluted) automatictransmission fluid is limited by the relationship between viscosityincrease of the fluid caused by the particles, and the temporary loss ofviscosity (associated with the particles) at maximum temperature andshear rate of fluid use. In general, the heat transfer improvement withthe ATF of the instant invention will be greater at room temperaturethan at the highest temperature of use due to the excellent viscosityindex of the particle-containing fluids, depending on the particle sizeand their thickening effect. Viscosity index is defined as therelationship of viscosity to the temperature of a fluid. It isdetermined by measuring the kinematic viscosities of the oil at 40° C.and 100° C. and using the tables or formulas included in ASTM D2270. Itis important to note that the smaller particles give the best thermalconductivity increase, and higher viscosity index of fluid, but alsocontribute to higher temporary viscosity loss in shear fields. A fluidmade with heat transfer improvement of 20% at 100° C. may have animprovement of 60% or more when compared to a conventional fluid at 40°C. Therefore the heat transfer improvement due to the particles may betwofold, due to the higher thermal conductivity of the particles, andalso due to the exceptional viscosity index of the particle-containingfluid.

It is an object of the present invention to provide a method ofpreparing a lubricant as a stable dispersion of the carbon nanomaterialsin a liquid medium with the combined use of dispersants/surfactants andphysical agitation.

It is an object of the present invention to provide a in which thecarbon nanomaterials are made from cost-effectivehigh-thermal-conductivity graphite (with thermal conductivity higherthan 80 W/m).

It is an object of the present invention to provide a method ofdeveloping a method of forming carbon nanomaterials from inexpensivebulk graphite.

It is an object of the present invention to provide a method ofutilizing carbon nanotube, graphite flakes, carbon fibrils, carbonparticles and combinations thereof.

It is an object of the present invention to provide a method of usingcarbon nanotubes which are either single-walled, or multi-walled, withtypical aspect ratio of 500-5000.

It is an object of the present invention whereby the carbon nanomaterialcan optionally be surface treated to be hydrophilic at surface for easeof dispersing into the aqueous medium.

It is an object of the present invention to provide a method wherein thesaid dispersants/surfactants are soluble or highly dispersible in thesaid liquid medium.

It is an object of the present invention to provide a process forpreparing a lubricant composition containing nanomaterial by

a) dissolving the said dispersants/surfactants or dispersant additivepackage into the base fluid; b) adding a high concentration (5-20% byweight) of the said carbon nanomaterials into the above mixture whilebeing strongly agitated by high impact milling, and/or ultrasonication,to form a pasty liquid; and c) the pasty liquid obtained in b) isfurther diluted with base oil and additives as needed to make the finallubricant.

It is an object of the present invention to provide a method of using aliquid medium selected from a natural oil (vegetable or animal oil), ora synthetic oil, or a mineral oil or a combination thereof.

It is an object of the present invention to provide a method of definingan appropriate dispersants/surfactants for a liquid medium of the typeused in the lubricant industry, whereby it is a surfactant or a mixtureof surfactants with low HLB value (<8), preferably nonionic or mixtureof nonionic and ionic surfactants.

It is an object of the present invention to provide that the dispersantscan be the ashless polymeric dispersants used in the lubricant industry.

It is an object of the present invention to provide a uniform dispersionin the form of a gel or paste with designed viscosity of carbonnanomaterials in base oil medium.

It is an object of the present invention to provide a uniform dispersionin a form as a gel or paste of high thermal conductivity graphitenanoparticle in petroleum, natural, or synthetic liquid medium.

It is an object of the present invention to provide a uniform dispersionin its final form as an automatic transmission fluid of relatively lowviscosity (kinematic viscosity less than 10 centistokes at 100° C.).

It is an object of the present invention to provide a uniform and stabledispersion in a form containing dissolved non-dispersing, otherfunctional compounds in the liquid medium.

It is an object of the present invention to provide a uniform and stabledispersion in a form without polymeric viscosity index improvers, whereall viscosity index improvement comes from the carbon nanomaterials.

It is an object of the present invention to provide a uniform and stabledispersion where due to the absence of polymeric materials thedispersion exhibits no permanent, only temporary loss in viscosity dueto shear fields and turbulence.

It is an object of the present invention to provide a uniform and stabledispersion where the carbon nanomaterials are used to convey anextremely high viscosity index, >200, and even >300.

It is an object of the present invention to provide a uniform and stabledispersion where the thermal conductivity and heat transfer capabilityof the fluid is at least more than 20% improved compared to conventionalmineral oil based automatic transmission fluids.

Other objects, features, and advantages of the invention will beapparent with the following detailed description taken in conjunctionwith the accompanying drawings showing a preferred embodiment of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the present invention will be had uponreference to the following description in conjunction with theaccompanying drawings in which like numerals refer to like partsthroughout the several views and wherein:

FIG. 1 is an atomic force microscopy (AFM) picture of an automatictransmission fluid composition showing the graphite nanoparticles asflakes or plate-like structures with an average diameter of around 50 nmand thickness around 5 nm.

FIG. 2 is a diagram of a hot-wire rig constructed to obtain the absolutemeasurement of the thermal conductivity of electrically conductingliquids by the transient hot-wire method.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention provides a graphitic dispersion in fluid mediumthat gives a high thermal conductivity and improved heat transfercapability compared to conventional fluids of the same medium. In thepresent invention the fluid medium is targeted in its viscosity,friction, and antioxidant characteristics to perform in modern automatictransmissions.

One preferred type of graphitic particles are carbon nanotubes, thenanotubes can be either single-walled, or multi-walled, having a typicalnanoscale diameter of 1-200 nanometers. More typically the diameter isaround 10-30 nanometers. The length of the tube can be in submicron andmicron scale, usually from 500 nanometers to 500 microns. More typicallength is 1 micron to 100 microns. The aspect ratio of the tube can befrom hundreds to thousands, more typical 500 to 5000. The surface of thenanotube can be treated chemically to achieve certain level ofhydrophilicity, or left as is from the production. Unfortunately, thecommercial availability of the prepared nanotubes is limited making themtoo expensive for incorporation into commodity type lubricants at thistime.

Therefor, a novel method has been developed to form nanomaterialssuitable for use with commodity type lubricants at a low cost andcapable of being produced in a large quantity using readily availableequipment. Other acceptable form of graphite is ahigh-thermal-conductivity graphite commercially available, e.g. POCOFOAM, available from Poco Graphite, Inc., and graphite powders availablefrom UCAR Carbon Company Inc. POCO FOAM is a high thermal conductivityfoamed graphite, thermal conductivity typically in the range 100 to 150W/m. A readily commercially available graphite is graphite powders fromUCAR Carbon Company Inc., thermal conductivity of 10 to 500 W/m, andtypically >80 W/m. Still another acceptable form of graphite is thehigh-thermal-conductivity graphite, Part#875G, from The Carbide/GraphiteGroup, Inc.

These graphite are prepared for the instant invention by pulverizing toa fine powder, dispersing chemically and physically in a fluid ofchoice, and then ball milled or otherwise size reduced until particle,flake, fibril or combinations thereof produce nanomaterial of a size ofless than 500 nm mean size is attained. The preferred method is todisperse the graphite by ball milling in a viscous fluid of mostadditives (detergents, dispersants, etc.) and then diluting the obtainedconcentrate with base oil and other additives as needed to attain thefinal viscosity and performance characteristics. The finer the particlesize attained upon milling, the better the thermal conductivity increasebut also the more viscosity thickening effect of the pasty concentrateon the final blend. These effects must be balanced to attain a suitablelubricating film thickness at the maximum shear rate and temperature offluid use. In general, any high thermal conductivity graphite can beused, provided that pulverization, milling and other described chemicaland physical methods can be used to reduce the size of the finalgraphite dispersion to below a mean particle size of 500 nm or less.

In the process of making lubricating fluid such as the automatictransmission fluid with the nanomaterial, the mechanical process andsequence of adding the components are important in order to fully takeadvantage of the high viscosity index of the nanoparticles an to makethe final fluid product with exceptionally high viscosity index. Highimpact mixing is necessary to achieve a homogeneous dispersion. Ballmill is one of the examples of a high impact mixer. In the instantinvention, an Eiger Mini Mill (Model: M250-VSE-EXP) is used as the highimpact ball mill. It utilizes high wear resistant zirconia beads as thegrinding media and circulates the dispersion constantly during milling.

To achieve the best milling effect and therefore the best viscosityindex improvement, the proper milling procedure has been developed.Firstly a 5% to 20% by weight of graphite powders, and more preferably10% by weight of graphite powders, in base oil dispersion is milled intoa paste state. Usually this step takes about 3 to 4 hours. Then add theappropriate effective amount of at least one dispersing agent(s),usually 1 to 2 times of the weight of graphite, into the mill. With theaddition of dispersing agent(s) the paste changes from paste into liquidalmost instantly, and extended milling becomes possible. For most casesthe extended milling period is 4 hours. It should be pointed out that ifthe mixture in the mill turns into a paste, the recirculation of itbecomes very difficult and thus a poor milling is resulted. It is alsofound that if the dispersing agent(s) is(are) added into the mill at thevery beginning, the viscosity index of the final nanofluids made fromthe milling process is not as high.

Graphite nanomaterials are obtained by pulverizing big graphite chunksweight several pounds or kilograms obtained from The Carbide/GraphiteGroup. The resulting pulverized material is size-selected through a meshfilter to be less than 75 Thirty (30) grams of the above pulverizedgraphite particles and 270 grams of a base oil, DURASYN 162 (acommercial 2 centistokes polyalphaolefin) were added into the Eiger MiniMill (Model: M250-VSE-EXP). The milling speed was gradually increased to4000 rpm. In about 4 hours the above mixture turned into thick paste.About 60 grams of this paste was discharged and labeled Paste ‘A’.Forty-eight (48) grams of a dispersant package from Lubrizol, LUBRIZOL9677MX, was added to the rest of the mixture in the mill. The pastebecame very thin, and successful recirculation was restored. Stopped themill after another 4 hours of milling and labeled the discharged pasteas Paste B. Paste C was obtained by milling a mixture of 30 grams ofgraphite with diameter less than 7560 grams of LUBRIZOL 9677MX, and 270grams of DURASYN 162 at 4000 rpm for 8 hours Note here the dispersingagent LUBRIZOL 9677MX was added into the mill at the very beginning.Then three automatic transmission fluids were formulated, A through C,using the above three pastes as concentrates respectively. The finalcompositions were exactly the same by weight and ingredients except forthe graphite material: 2% graphite, 4% LUBRIZOL 9677 MX, 18% DURASYN162, 76% DURASYN 166 (a commercial 6 centistokes polyalphaolefin baseoil) (all percentage by weight). Example 1 illustrates the 100° C.viscosity and viscosity index (VI) of the fluids. It was also found thatthe graphite particle size before milling was an important variable tocontrol the viscosity modification effect as well. For example, startingwith graphite smaller than 10 (obtained as graphite powder from UCARCarbon Company Inc.) and following the same procedure as Paste B, a thinPaste D was obtained. An automatic transmission fluid D was formulationwith the same composition as ATF A and result is list in Example 1 aswell. The particle size is measured by atomic force microscopy (AFM),and FIG. 1 illustrates an AFM picture of ATF B. The graphitenanoparticles appear to be flakes or a plate-like structure, withaverage diameter of around 50 nm and thickness around 5 nm.

Oil Basestocks

The petroleum liquid medium can be any petroleum distillates orsynthetic petroleum oils, greases, gels, or oil-soluble polymercomposition. More typically, it is the mineral basestocks or syntheticbasestocks used in the lube industry, e.g., Group I (solvent refinedmineral oils). Group II (hydrocracked mineral oils), Group III (severelyhydrocracked oils, sometimes described as synthetic or semi-syntheticoils), Group IV (polyalphaolefins), and Group V (esters, naphthenes, andothers). One preferred group includes the polyalphaolefins, syntheticesters, and polyalkylglycols.

Synthetic lubricating oils include hydrocarbon oils and halo-substitutedhydrocarbon oils such as polymerized and interpolymerized olefins (e.g.,polybutylenes, polypropylenes, propylene-isobutylene copolymers,chlorinated polybutylenes, poly(l-octenes), poly(l-decenes), etc., andmixtures thereof; alkylbenzenes (e.g., dodecylbenzenes,tetradecylbenzenes, dinonylbenzenes, di-(2-ethylhexyl)benzenes, etc.);polyphenyls (e.g., biphenyls, terphenyls, alkylated polyphenyls, etc.),alkylated diphenyl, ethers and alkylated diphenyl sulfides and thederivatives, analogs and homologs thereof and the like. Alkylene oxidepolymers and interpolymers and derivatives thereof where the terminalhydroxyl groups have been modified by esterification, etherification,etc. constitute another class of known synthetic oils.

Another suitable class of synthetic oils comprises the esters ofdicarboxylic acids (e.g., phtalic acid, succinic acid, alkyl succinicacids and alkenyl succinic acids, maleic acid, azelaic acid, subericacid, sebacic acid, fumaric acid, adipic acid, alkenyl malonic acids,etc.) with a variety of alcohols (e.g., butyl alcohol, hexyl alcohol,dodecyl alcohol, 2-ethylhexyl alcohol, ethylene glycol diethylene glycolmonoether, propylene glycol, etc.). Specific examples of these estersinclude dibutyl adipate, di(2-ethylhexyl) sebacate, di-hexyl fumarate,dioctyl sebacate, diisooctyl azelate, diisodecyl azealate, dioctylphthalate, didecyl phthalate, dicicosyl sebacate, the 2-ethylhexyldiester of linoleic acid dimer, the complex ester formed by reacting onemole of sebacic acid with two moles of tetraethylene glycol and twomoles of 2-ethylhexanoic acid, and the like.

Esters useful as synthetic oils also include those made from C C₁₂monocarboxylic acids and polyols and polyol ethers such as neopentylglycol, trimethylolpropane, pentaerythritol, dipentaerythritol,tripentaerythritol, etc. Other synthetic oils include liquid esters ofphosphorus-containing acids (e.g., tricresyl phosphate, trioctylphosphate, diethyl ester of decylphosphonic acid, etc.), polymerictetrahydrofurans and the like.

Preferred polyalphaolefins (PAO), include those sold by Mobil ChemicalCompany as SHF fluids, and those sold by Ethyl Corporation under thename ETHYLFLO, or ALBERMARLE. PAO include the ETHYL-FLOW series by EthylCorporation, “Albermarle Corporation,” including ETHYL-FLOW 162, 164,166, 168, and 174, having varying viscosity from about 2 to about 460centistokes.

Mobil SHF-42 from Mobil Chemical Company, EMERY 3004 and 3006, andQuantum Chemical Company provide additional polyalphaolefins basestocks.For instance, EMERY 3004 polyalphaolefin has a viscosity of 3.86centistokes at (100° C.) and 16.75 centistokes at (40° C.). It has aviscosity index of 125 and a pour point of −98° C. Moreover, EMERY 3006polyalphaolefin has a viscosity of 5.88 centistokes at 212° C. and 31.22centistokes at 104° C. It has a viscosity index of 135 and a pour pointof −87° C.

Additional satisfactory polyalphaolefins are those sold by Uniroyal Inc.under the brand SYNTON PAO-40, which is a 40 centistokespolyalphaolefin. Also useful are the Oronite brand polyalphaolefinsmanufactured by Chevron Chemical Company.

It is contemplated that Gulf SYNFLUID 4 centistokes PAO; commerciallyavailable from Gulf Oil Chemicals Company, a subsidiary of ChevronCorporation, which is similar in many respects to EMERY 3004 may also beutilized herein. MOBIL SHF-41 PAO, commercially available from MobilChemical Corporation, is also similar in many respects to EMERY 3004.

Preferably the polyalphaolefins will have a viscosity in the range ofabout 2-100 centistokes at 100° C., with viscosity of 4 and 10centistokes being particularly preferred.

The most preferred synthetic base oil ester additives are polyolestersand diesters such as di-aliphatic diesters of alkyl carboxylic acidssuch as di-2-ethylhexylazelate, di-isodecyladipate, anddi-tridecyladipate, commercially available under the brand name EMERY2960 by Emery Chemicals, described in U.S. Pat. No. 4,859,352 toWaynick. Other suitable polyolesters are manufactured by Mobil Oil.Mobil polyolesters P-43, M Ø45 containing two alcohols, and Hatco Corp.2939 are particularly preferred.

Diesters and other synthetic oils have been used as replacements ofmineral oil in fluid lubricants. Diesters have outstanding extreme lowtemperature flow properties and good resistance to oxidative breakdown.

The diester oil may include an aliphatic diester of a dicarboxylic acid,or the diester oil can comprise a dialkyl aliphatic diester of an alkyldicarboxylic acid, such as di-2-ethyl hexyl azelate, di-isodecylazelate, di-tridecyl azelate, di-isodecyl adipate, di-tridecyl adipate.For instance, Di-2-ethylhexyl azelate is commercially available underthe brand name of EMERY 2958 by Emery Chemicals.

Also useful are polyol esters such as EMERY 2935, 2936, and 2939 fromEmery Group of Henkel Corporation and Hatco 2352, 2962, 2925, 2938,2939, 2970, 3178, and 4322 polyol esters from Hatco Corporation,described in U.S. Pat. No. 5,344,579 to Ohtani et al., and Mobil ester P24 from Mobil Chemical Company. Mobil esters such as made by reactingdicarboxylic acids, glycols, and either monobasic acids or monohydricalcohols like EMERY 2936 synthetic-lubricant basestocks from QuantumChemical Corporation and Mobil P 24 from Mobil Chemical Company can beused. Polyol esters have good oxidation and hydrolytic stability. Thepolyol ester for use herein preferably has a pour point of about −100°C. or lower to −40° C. and a viscosity of about 2-460 centistokes at100° C.

Group III oils are often referred to as hydrogenated oil to be used asthe sole base oil component of the instant invention providing superiorperformance to conventional ATFs with no other synthetic oil base ormineral oil base.

A hydrogenated oil is a mineral oil subjected to hydrogenation orhydrocracking under special conditions to remove undesirable chemicalcompositions and impurities resulting in a mineral oil based oil havingsynthetic oil components and properties. Typically the hydrogenated oilis defined as a Group III petroleum based stock with a sulfur level lessthan 0.03, severely hydrotreated and isodewaxed with saturates greaterthan or equal to 90 and a viscosity index of greater than or equal to120, and may optionally be utilized in amounts up to 90 percent byvolume, more preferably from 5.0 to 50 percent by volume and morepreferably from 20 to 40 percent by volume when used in combination witha synthetic or mineral oil.

The hydrogenated oil my be used as the sole base oil component of theinstant invention providing superior performance to conventional motoroils with no other synthetic oil base or mineral oil base. When used incombination with another conventional synthetic oil such as thosecontaining polyalphaolefins or esters, or when used in combination witha mineral oil, the hydrogenated oil may be present in an amount of up to95 percent by volume, more preferably from about 10 to 80 percent byvolume, more preferably from 20 to 60 percent by volume and mostpreferably from 10 to 30 percent by volume of the base oil composition.

A Group I or II mineral oil basestock may be incorporated in the presentinvention as a portion of the concentrate or a basestock to which theconcentrate may be added. Preferred as mineral oil basestocks are theMarathon Ashland Petroleum (MAP) 325 Neutral defined as a solventrefined neutral having a Sabolt Universal viscosity of 325 SUS at 100°C. and MAP 100 Neutral defined as a solvent refined neutral having aSabolt Universal viscosity of 100 SUS at 100° C., both manufactured bythe Marathon Ashland Petroleum.

Other acceptable petroleum-base fluid compositions include whitemineral, paraffinic and MVI naphthenic oils having the viscosity rangeof about 20-400 centistokes. Preferred white mineral oils include thoseavailable from Witco Corporation, Arco Chemical Company, PSI andPenreco. Preferred paraffinic oils include solvent neutral oilsavailable from Exxon Chemical Company, HVI neutral oils available fromShell Chemical Company, and solvent treated neutral oils available fromArco Chemical Company. Preferred MVI naphthenic oils include solventextracted coastal pale oils available from Exxon Chemical Company, MVIextracted/acid treated oils available from Shell Chemical Company, andnaphthenic oils sold under the names HYDROCAL and CALSOL by Calumet, anddescribed in U.S. Pat. No. 5,348,668 to Oldiges.

Finally, vegetable oils may also be utilizes as the liquid medium in theinstant invention. Soybean or rapeseed oil, particularly of the higholeic or mid oleic genetically engineered type, commercially availablefrom Archer Daniels Midland Company, are good examples of these oils.Soybean oil is of interest because it has a high thermal conductivityitself.

Dispersants Used in Lubricant Industry

Dispersants used in the lubricant industry are typically used todisperse the “cold sludge” formed in gasoline and diesel engines, whichcan be either “ashless dispersants”, or containing metal atoms. They canbe used in the instant invention since they are found to be an excellentdispersing agent for nanoparticles with graphitic structure of thisinvention. They are also needed to disperse wear debris and products oflubricant degradation within the transmission.

The ashless dispersants commonly used in the automotive industry containan lipophilic hydrocarbon group and a polar functional hydrophilicgroup. The polar functional group can be of the class of carboxylate,ester, amine, amide, imine, imide, hydroxyl, ether, epoxide, phosphorus,ester carboxyl, anhydride, or nitrile. The lipophilic group can beoligomeric or polymeric in nature, usually from 70 to 200 carbon atomsto ensure oil solubility. Hydrocarbon polymers treated with variousreagents to introduce polar functions include products prepared bytreating polyolefins such as polyisobutene first with maleic anhydride,or phosphorus sulfide or chloride, or by thermal treatment, and thenwith reagents such as polyamine, amine, ethylene oxide, etc.

Of these ashless dispersants the ones typically used in the petroleumindustry include N-substituted polyisobutenyl succinimides andsuccinates, alkyl methacrylate-vinyl pyrrolidinone copolymers, alkylmethacrylate-dialkylaminoethyl methacrylate copolymers,alkylmethacrylate-polyethylene glycol methacrylate copolymers, andpolystearamides. Preferred oil-based dispersants that are most importantin the instant application include dispersants from the chemical classesof alkylsuccinimide, succinate esters, high molecular weight amines,Mannich base and phosphoric acid derivatives. Some specific examples arepolyisobutenyl succinimide-polyethylenepolyamine, polyisobutenylsuccinic ester, polyisobutenyl hydroxybenzyl-polyethylenepolyamine,bis-hydroxypropyl phosphorate. Commercial dispersants suitable fortransmission fluid are for example, Lubrizol 890 (an ashless PIBsuccinimide), Lubrizol 6420 (a high molecular weight PIB succinimide),ETHYL HITEC 646 (a non-boronated PIB succinimide). The dispersant may becombined with other additives used in the lubricant industry to form aispersant-detergent (DI) additive package for transmission fluids, e.g.,LUBRIZOL 9677MX, and the whole DI package can be used as dispersingagent for the nanoparticle dispersions.

Other Types of Dispersants

Alternatively a surfactant or a mixture of surfactants with low HLBvalue (typically less than or equal to 8), preferably nonionic, or amixture of nonionics and ionics, may be used in the instant invention.

The dispersants selected should be soluble or dispersible in the liquidmedium. The dispersant can be in a range of up from 0.01 to 30 percent,more preferably in a range of from between 0.5 percent to 20 percent,more preferably in a range of from between 1 to 15 percent, and mostpreferably in a range of from between 2 to 13 percent. The carbonnanomaterials can be of any desired weight percentage in a range of from0.001 up to 10 percent. For practical application it is usually in arange of from between 0.01 percent to 10 percent, and most preferably ina range of from between 0.1 percent to 5 percent. The remainder of theformula is the selected medium.

It is believed that in the instant invention the dispersant functions byadsorbing onto the surface of the carbon nanomaterials.

Other Chemical Compounds

This dispersion may also contain a large amount of one or more otherchemical compounds, preferably polymers, not for the purpose ofdispersing, but to achieve thickening or other desired fluidcharacteristics. These can be added but reduce the amount of particulatethat can be used without excessive thickening.

The viscosity improvers used in the lubricant industry can be used inthe instant invention for the oil medium, which include olefincopolymers (OCP), polymethacrylates (PMA), hydrogenated styrene-diene(STD), and styrene-polyester (STPE) polymers. Olefin copolymers arerubber-like materials prepared from ethylene and propylene mixturesthrough vanadium-based Ziegler-Natta catalysis. Styrene-diene polymersare produced by anionic polymerization of styrene and butadiene orisoprene. Polymethacrylates are produced by free radical polymerizationof alkyl methacrylates. Styrene-polyester polymers are prepared by firstco-polymerizing styrene and maleic anhydride and then esterifying theintermediate using a mixture of alcohols.

Other compounds which can be used in the instant invention in the oilmedium include: acrylic polymers such as polyacrylic acid and sodiumpolyacrylate, high-molecular-weight polymers of ethylene oxide such asPolyox WSR from Union Carbide, cellulose compounds such ascarboxymethylcellulose, polyvinyl alcohol (PVA), polyvinyl pyrrolidone(PVP), xanthan gums and guar gums, polysaccharides, alkanolamides, aminesalts of polyamide such as DISPARLON AQ series from King Industries,hydrophobically modified ethylene oxide urethane (e.g., ACRYSOL seriesfrom Rohmax), silicates, and fillers such as mica, silicas, cellulose,wood flour, clays (including organoclays) and nanoclays, and resinpolymers such as polyvinyl butyral resins, polyurethane resins, acrylicresins and epoxy resins.

Chemical compounds such as seal swell agents or plasticizers can also beused in the instant invention and may be selected from the groupincluding phthalate, Adipate, sebacate esters, and more particularly:glyceryl tri(acetoxystearate), epoxidized soybean oil, epoxidizedlinseed oil, N,n-butyl benzene sulfonamide, aliphatic polyurethane,epoxidized soy oil, polyester glutarate, polyester glutarate,triethylene glycol caprate/caprylate, long chain alkyl ether, dialkyldiester glutarate, monomeric, polymer, and epoxy plasticizers, polyesterbased on adipic acid, hydrogenated dimer acid, distilled dimer acid,polymerized fatty acid trimer, ethyl ester of hydrolyzed collagen,isostearic acid and sorbian oleate and cocoyl hydrolyzed keratin,PPG-12/PEG-65 lanolin oil, dialkyl adipate, alkylaryl phosphate, alkyldiaryl phosphate, modified triaryl phosphate, triaryl phosphate, butylbenzyl phthalate, octyl benzyl phthalate. alkyl benzyl phthalate,dibutoxy ethoxy ethyl adipate, 2-ethylhexyldiphenyl phosphate, dibutoxyethoxy ethyl formyl, diisopropyl adipate, diisopropyl sebacate, isodecyloieate, neopentyl glycol dicaprate, neopenty giycol diotanoate, isohexylneopentanoate, ethoxylated lanolins, polyoxyethylene cholesterol,propoxylated (2 moles) lanolin alcohols, propoxylated lanoline alcohols,acetylated polyoxyethylene derivatives of lanoline, anddimethylpolysiloxane. Other plasticizers which may be substituted forand/or used with the above plasticizers including glycerine,polyethylene glycol, dibutyl phthalate, and2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, and diisononylphthalate all of which are soluble in a solvent carrier. Other sealswelling agents such as Lubrizol 730 can also be used.

Antioxidants are an important part of transmission fluids. Generalclasses include zinc

dialkyldithiophosphates, alkyl and aryl phenols, alkyl and aryl amines,and sulfurized olefins. Commercial examples are Ciba L57 (phenyl amine)and Etnyl Hitec 1656.

Pour point depressants, either of polymethyl methacrylate or ethylenepropylene olefin co-polymer type are useful to decrease the lowtemperature Brookfield viscosity of the ATF. Examples include ROHMAX3008, ROHMAX 1-333, LUBRIZOL 6662A.

Friction Modifiers are used to control friction and torquecharacteristics of the fluid. Commercial examples include LUBRIZOL 8650and HITEC 3191.

Physical Agitation

The physical mixing includes high shear mixing, such as with a highspeed mixer, homogenizers, microfluidizers, a Kady mill, a colloid mill,etc., high impact mixing, such as attritor, ball and pebble mill, etc.,and ultrasonication methods or passing through a small orifice such as afuel injector. Turbulent flows of any type will assist mixing.

Ball milling is the most preferred physical method in the instantinvention since it is effective at rapidly reducing the graphiteparticles to very small size while simultaneously dispersing them into aconcentrated paste as previously described. The concentrate can then bediluted with base oil and other additives to hit a final targetviscosity, depending on the maximum temperature and shear conditionsanticipated in the target transmission. For further size reduction andreducing particle maximum size the diluted oil can be passed through asmall orifice such as a fuel injector. The raw material mixture may bepulverized by any suitable known dry or wet grinding method. Onegrinding method includes pulverizing the raw material mixture in thefluid mixture of the instant invention to obtain the concentrate, andthe pulverized product may then be dispersed further in a liquid mediumwith the aid of the dispersants described above. However, pulverizationor milling reduces the carbon nanotube average aspect ratio. A detaileddescription has been given in an earlier section of the instantinvention.

Ultrasonication is another physical method in the instant inventionsince it is less destructive to the carbon nanomaterial structure thanthe other methods described. Ultrasonication can be done either in thebath-type ultrasonicator, or by the horn-type ultrasonicator. Moretypically, horn-type ultrasonication is applied for higher energyoutput. Sonication at the medium-high instrumental intensity for up to30 minutes, and usually in a range of from 10 to 20 minutes is desiredto achieve better homogeneity.

The instant method of forming a stable dispersion of carbonnanomaterials in a solution consist of three steps. First select theappropriate concentrate of dispersant or mixture of dispersing and otheradditives for the carbon nanomaterials, and the medium, and dissolve thedispersant into the liquid medium to form a concentrate solution(keeping in mind the final additive concentrations desired followingdilution); secondly add a high concentration of the carbon nanomaterialsinto the dispersant-containing solution, initiate strongly agitating,ball milling, or ultrasonicating, or any combination of physical methodsnamed; following an agitation time of several hours, the resulting pastewill be extremely stable and easily dilutable into more base oil andadditives to give the final desired concentrations of additives and thedesired final viscosity.

EXAMPLES

The following examples describe preferred embodiments of the invention.Other embodiments within the scope of the claims herein will be apparentto one skilled in the art from consideration of the specification orpractice of the invention as disclosed herein. It is intended that thespecification, together with the examples, be considered exemplary only,with the scope and spirit of the invention being indicated by the claimswhich follow the examples. In the examples all percentages are given ona weight basis unless otherwise indicated. Reference to documents madein the specification is intended to result in such patents or literaturecited are expressly incorporated herein by reference, including anypatents or other literature references cited within such documents as iffully set forth in this specification.

Example 1 Automatic Transmission Fluids and Viscosity Data

ATF A B C D E* From Concentrate Paste Paste Paste Paste N/A A B C DKinematic 7.55 19.68 10.83 7.48 7.15 viscosity at 100° C., cSt Kinematicvis- 28.44 29.32 28.77 27.85 33.67 cosity at 40° C., cSt Viscosity Index254 634 395 257 183 *E is an off-the-shelf regular commercial ATF(MERCON V).

Thermal conductivity is measured by a transient hot-wire rig constructedby the inventors in-house according to Nagasaka et al. (Y. Nagasaka andA. Nagashima, Absolute measurement of the thermal conductivity ofelectrically conducting liquids by the transient

${R\; H\; T\; E\; F} = {\left( \frac{k}{k_{0}} \right)^{0.67}\left( \frac{\eta}{\eta_{0}} \right)^{- 0.52}\left( \frac{\rho}{\rho_{0}} \right)^{0.57}\left( \frac{C_{P}}{C_{P,0}} \right)^{0.33}}$

hot-wire method, Journal of Physics E: Sci. Instrum. 1981, 14,1435-1440). A diagram of the rig is shown in FIG. 2. The relative heattransfer efficiency factor (RHTEF) of a test fluid versus a another testfluid (denoted by subscript 0) is evaluated by the above equation.

Example 2

Components Description Weight percentage Carbon nanomaterial Graphite(The 2.0 Carbide/Graphite Group, Inc.) Dispersant Lubrizol 9677MX 4.0Base oil Durasyn 166 76.0 Base oil Durasyn 162 18.0 Process Pulverize to<75 and then Eiger mini mill Viscosity 40 (cSt) 28.4 Viscosity 100 (cSt)7.55 Viscosity Index (VI) 254 (vs. 183 for conventional ATF) Thermalconductivity 0.1776 (vs. 0.132 for conventional ATF) (W/m) RHTEF at 401.4 (vs. conventional ATF)

Example 3

Components Description Weight percentage Carbon nanomaterial Graphitepowder 2.0 (UCAR) Dispersant Lubrizol 9677MX 4.0 Base oil Durasyn 16676.0 Base oil Durasyn 162 18.0 Process Eiger mini mill Viscosity 40(cSt) 27.85 Viscosity 100 (cSt) 7.48 Viscosity Index (VI) 257 (vs. 183for conventional ATF) Thermal conductivity 0.1926 (vs. 0.132 forconventional ATF) (W/m) RHTEF at 40 1.5 (vs. conventional ATF)

Example 4

Components Description Weight percentage Carbon nanomaterial Poco Foam(Poco 2.5 Graphite) Dispersant Lubrizol 9677MX 7.5 Base oil SK Yubase 442.5 Base oil SK Yubase 3L 42.5 Viscosity modifier Lubrizol 7720C 5.0Process Eiger mini mill Viscosity 40 (cSt) 43.12 Viscosity 100 (cSt)9.55 Viscosity Index (VI) 215 (vs. 183 for conventional ATF) Thermalconductivity 0 . . . 2092 vs. 0.132 for conventional ATF) (W/m) RHTEF at40 1.6 (vs. conventional ATF)

Example 5

Components Description Weight percentage Carbon nanomaterial Graphite(The 2.0 Carbide/Graphite Group, Inc.) Dispersant Lubrizol 9677MX 5.0Base oil Durasyn 162 18.0 Base oil Hatco HXL-7156 37.5 Base oil SKYubase L3 37.5 Process Pulverize to <75 then EIGER mini-mill Viscosity40 (cSt) 35.18 Viscosity 100 (cSt) 10.48 Viscosity Index (VI) 306 (vs.183 for conventional ATF) Thermal conductivity 0.1889 vs. 0.132 forconventional ATF) (W/m) RHTEF at 40 1.3 (vs. conventional ATF)

Example 6

MerconV MaxLife Parameters ATF ATF Fluid #1 Fluid #2 Fluid #3 Fluid #4 %Graphite (UCAR) 0 0 2.0 0 2.0 0 % Graphite (Poco Foam) 0 0 0 2.0 0 2.0 %DI Package 10.5 10.5 4.0 6.5 10.5 10.5 40 Vis (cSt) 36.2 34.56 27.8927.44 16.01 16.96 100 Vis (cSt) 7.7 7.12 7.48 7.35 7.57 7.37 ViscosityIndex 190 175 257 255 527 475 100 C_(p) (J/g) 2.1801 1.9706 2.255 2.2772.0867 2.1578 20 Density (g/cm 0.8632 0.8389 0.8244 0.8294 0.8213 0.822640 Density (g/cm 0.8502 0.8288 0.8151 0.8191 0.8099 0.8114 100 Density(g/cm 0.8115 0.7921 0.7781 0.7828 0.7746 0.7758 RHTEF at 40 1 (baseline)N/A 1.46 1.54 1.8 1.82 RHTEF at 100 1 (baseline) N/A 1.27 1.34 1.17 1.24

Example 7

Components Description Weight percentage Carbon nanomaterialMulti-walled carbon 0.2 nanotubes Dispersant Oronite OLOA 9061 4.8 Baseoil Durasyn 166 95.0 Process Ultrasonicate for 15 minutes and then passthe dispersion through a fuel injector shear nozzles 20 cycles Viscosity40 (cSt) 46.08 Viscosity 100 (cSt) 9.89 Viscosity Index (VI) 208 (vs.183 for conventional ATF) Thermal conductivity 0.1522 vs. 0.132 forconventional ATF) (W/m) RHTEF at 40 1.2 (vs. conventional ATF)

The foregoing detailed description is given primarily for clearness ofunderstanding and no unnecessary limitations are to be understoodtherefrom, for modification will become obvious to those skilled in theart upon reading this disclosure and may be made upon departing from thespirit of the invention and scope of the appended claims. Accordingly,this invention is not intended to be limited by the specificexemplification presented herein above. Rather, what is intended to becovered is within the spirit and scope of the appended claims.

1. A method of preparing a lubricant as a stable dispersion of thecarbon nanomaterials in a liquid medium with the combined use ofdispersants/surfactants and physical agitation, comprising the steps of:a) dissolving an effective amount of at least one of the groupconsisting of a dispersant, a surfactant, a dispersant additive package,and combinations thereof into an effective amount of at least one baseoil forming a first mixture; b) adding a high concentration of up to 20percent by weight of a carbon nanomaterial into said first mixture whilebeing strongly agitated by high impact milling, and/or ultrasonication,to form a pasty liquid; and c) diluting said pasty liquid with aneffective amount of a base oil.